Heat transfer for heat pump water heater

ABSTRACT

A water heater is provided that improves heat transfer between the coils of the heat exchanger of a refrigerant-based heating system and the water in the heater&#39;s water tank. Grooves can be added to the exterior of the water tank. The coils of the heat exchanger are positioned within the grooves on the exterior surface of the water tank. Additional features may also be used to further improve heat transfer. Methods for constructing such water heater are also provided.

FIELD OF THE INVENTION

The subject matter of the present disclosure relates generally to a heat pump water heater having a tank designed to allow for improved heat transfer between the heat pump condenser and water in the tank.

BACKGROUND OF THE INVENTION

Water heaters can provide for the heating and storage of water to be used in e.g., a residential or commercial structure. While water heaters can be provided in a variety of shapes and sizes, a typical shape includes an elongated cylindrical tank. In some water heaters, the tank may be configured for a vertically upright position and be surrounded by insulation and an exterior wrapper or jacket. A heat source is provided for raising the temperature of water in the tank. The heat energy may be supplied e.g., by gas burners, electrically-resistant coils, and/or a heat pump using a refrigerant cycle.

In one construction, a water heater using a refrigerant-based heat pump heats the water in the water tank by wrapping a plurality of coils around the cylindrical exterior wall of the water tank. The coils serve as a heat exchanger, also referred to as a condenser, through which hot refrigerant flows around the tank. This configuration enables heat transfer from the hot refrigerant, through the coils and the tank walls, and then to the water.

Certain challenges exist with this construction, however. Such construction, for example, can be an inefficient means of heat transfer between the coils and the water tank. Because the coils in such construction have limited contact with the walls of water tank, the heat transfer efficiency is limited. In an effort to compensate for this inefficiency, some constructions may use longer coils to increase the total amount of contact for heat transfer between the coils and the tank. Unfortunately, this adds to the cost of the water heater system. In addition certain challenges exist with the efficiency of the heat transfer to the water from the tank. The film coefficient of the water at the tank surface is the key factor in the effectiveness of the convective heat transfer from the tank to the water.

Accordingly, a water heater using a refrigerant-based heating system having one or more features that can improve heat transfer between the heating system and the water in the tank would be useful. More particularly, such a water heater that can provide increased surface area for contact between the coils of the heat exchanger and the water tank over a given length of coil would be beneficial. A method of creating the tank for such a water heater would also useful.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a water heater that improves heat transfer between the coils of the heat exchanger of a refrigerant-based heating system and the water contained in the heater's water tank. Grooves can be added to the exterior of the water tank and thus can also form an analogous shape on the interior of the water tank. The coils of the heat exchanger can be positioned within the grooves on the exterior surface of the water tank. Such construction provides more surface area for contact between the coils and the tank for a given length of coil. Additional features as described herein may also be used to further improve heat transfer. Exemplary methods for constructing such a water heater are also provided. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In one exemplary embodiment, the present disclosure provides a water heater that includes a tank for holding water. The tank has a cylindrically-shaped wall connected between a pair of end portions and defines axial, radial, and circumferential directions. The exterior surface of the tank defines a plurality of circumferentially-extending grooves, spaced apart in the axial direction. A refrigerant-based heating system is configured for heating water in the tank. The heating system includes a heat exchanger having a plurality of coils for the flow of heated refrigerant. The coils extend around the tank and are positioned within the plurality of grooves defined by the exterior surface of the cylindrically-shaped wall.

In one exemplary aspect of the present disclosure, a method is provided for making a tank with grooves. This exemplary method includes providing a flat metal sheet, creating a plurality of grooves in the flat outer surface of the metal sheet, rolling up the metal sheet in such a manner so as to form the cylindrically-shaped wall of a tank, joining together the metal sheet, and adding a pair of end portions to complete the formation of the tank.

In another exemplary aspect of the present disclosure, an additional method is provided for making a tank with grooves. This exemplary method includes providing a tank having a cylindrically-shaped wall, connected between a pair of end portions, and creating a plurality of grooves along the cylindrically-shaped wall of the tank, spaced apart along the axial direction, and providing grooves along the interior surface and exterior surface of the tank.

In another exemplary embodiment, the present invention provides a water heater that includes a tank for holding water. The tank includes a cylindrically-shaped wall connected between a pair of end portions. The tank defines axial, circumferential, and radial directions. A plurality of heat transfer features project along the radial direction from an interior surface of the tank. The heat transfer features extend longitudinally along the axial direction of the tank and are spaced apart about the circumferential direction. The heat transfer features providing additional surface area for heat transfer with water contained in the tank. A refrigerant-based heating system is configured for heating water in the tank. The heating system includes a heat exchanger that includes a plurality of coils for the flow of heated refrigerant. The coils extend around the tank on the cylindrically-shaped wall.

These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 is a cross-sectional side view of an exemplary embodiment of a water heater of the present disclosure.

FIG. 2 is a close-up cross-sectional side view of the exemplary embodiment of a water heater of the present disclosure shown in FIG. 1.

FIG. 3 is a close-up view of the side of an exemplary embodiment of a tank used in a water heater of the present disclosure.

FIG. 4 illustrates steps of an exemplary method for making a tank with grooves.

FIG. 5 is a cross-sectional view of another exemplary embodiment of a tank used in a water heater of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 provides a cross-sectional view of an exemplary embodiment of a vertically oriented water heater 100 of the present disclosure. In this embodiment, water heater 100 includes a tank 124 for storing water. Tank 124 defines a radial direction R and a vertical direction V. In FIG. 1, vertical direction V runs parallel to the axial direction of tank 124.

Tank 124 has a cylindrically-shaped wall 176 extending between a pair of end portions or, more particularly, between a bottom portion 170 and a top portion 172. Wall 176 defines a circumferential direction C extending around tank 124. Bottom portion 170 includes a circular bottom edge 142. Top portion 172 includes a water outlet 122 with associated coupling 114 and a water inlet 120 with associated coupling 116. Coupling 114 connects with conduit 110, and coupling 116 connects with conduit 112, each extending through housing 102. In turn, conduits 110 and 112 can each be fitted with couplings 106 and 108, respectively, for connection of water heater 100 to the piping or plumbing associated with a water supply system of e.g., a commercial or residential structure. Coupling 108 would be connected with e.g., a pipe delivering a pressurized water supply that flows into tank 124 using dip tube 118. In turn, heated water is returned to such piping system through the connection provided by coupling 106.

Mounted to top 172 is housing 102, which houses refrigerant-based heating system 104. Heating system 104 employs coils 130 to circulate hot refrigerant around tank 124 and heat water in tank 124. Coils 130 operate as a heat exchanger or, more particularly, as a condenser for heating system 104. As will be understood by one of skill in the art, compressed refrigerant vapor flowing through coils 130 condenses to a liquid in coils 130 to provide heat to water in tank 124. Water heater 100 is provided by way of example only. Using the teachings disclosed herein it will be understood that other configurations, constructions, shapes for water heater 100 with heating system 104 may be used as well.

For reasons previously stated, it is desirable to increase the surface area for contact between coils 130 and tank 124. Such an increase will provide increased heat transfer between coils 130 and tank 124 for a given length of coil and can decrease the overall length of coils required to transfer heat from coils 130 to water in tank 124. In addition, it is desired to increase the surface area and shape of the tank 124 on the interior surface 177 in contact with water in tank 124. The increased surface area and changes in shape improve the contact area with the water and changes the film coefficient of convective heat transfer from the tank surface 124 to the water.

Accordingly, tank 124 has a plurality of grooves 174 formed along the exterior surface 178 of the cylindrically-shaped wall 176. As shown in FIG. 1 and more clearly in FIGS. 2 and 3, coils 130 from heating system 104 fit into grooves 174 in tank 124 so as to increase the surface area for contact between tank 124 and coils 130 for a given length of coil. Grooves 174 also appear on internal surface 177 and provide increased area for heat transfer with water in tank 124. Additionally, for this exemplary embodiment, grooves 174 may have a circularly-shaped surface 180 to accommodate coils 130. However, in other embodiments grooves 174 may have a surface that is e.g., U-shaped, V-shaped, or square shaped. Grooves 174 may have a depth D in radial direction R that is less than the diameter C of coils 130, so that coils 130 extend beyond exterior surface 178 of cylindrically-shaped wall 176 of tank 124. Alternatively, grooves 174 may have a depth D that is greater than the diameter C of coils 130. Grooves 174 may also have a width along vertical direction, V, approximately equal to the diameter of coils 130. Other configurations may be used as well.

In one exemplary embodiment, coils 130 may be affixed to tank 124 using a thermal paste that further improves heat transfer. In still another embodiment, coils 130 may be welded to tank 124. As in the exemplary embodiment shown in FIG. 1, grooves 174 and coils 130 may run along exterior surface 178 of cylindrically-shaped wall 176 of tank 124 in a helical manner in radial direction R.

In another exemplary embodiment and as shown in FIG. 1, tank 124 may be positioned within an outer jacket 98 that surrounds the tank to create an annular space 146 between tank 124 and jacket 98. Insulation 126 may be provided within annular space 146 to reduce the amount of heat transfer to the environment. Insulation 126 can be provided as foamed-in insulation, but other materials may be used as well.

In yet another exemplary embodiment of the present disclosure, the tank 124 of the water heater 100 could be mounted in a horizontal configuration as shown in FIG. 1 with the refrigerant-based heating system attached to either pair of end portions. In this configuration, the axial direction A of the tank 124 would be parallel to the vertical direction. However, other orientations could be used as well. For example, the axial direction A of tank could be parallel to the horizontal direction.

In yet another exemplary embodiment, the tank could be formed out of a process such that the interior surface of the tank has a plurality of internal heat transfer features—e.g., ribs, fins, or the like—that project into the tank and extend longitudinally along the axial direction of the tank. For example, FIG. 5 provides a cross-sectional view of another exemplary embodiment of tank 124 where a plurality of T-shaped fins 133 are spaced apart about the circumferential direction C of tank 124 and extend along radial direction R into tank 124. Fins 133 also extend longitudinally along the axial direction A of tank 124. Fins 133 could be added, for example, by welding or extruding the tank body with fins 133 in place. Internal features such as fins 133 can increase the rate of heat transfer to the water and improve the convective heat transfer film coefficient.

As indicated above, the present subject matter is generally directed to a water heater having a tank with grooves to allow for improved heat transfer between the coils and the tank, and methods for making the tank with grooves. As such, an exemplary method of constructing tank 124 is now described with reference to FIG. 4.

First, in step 300, a metal sheet 200 is provided having a flat outer surface 204 and a desired thickness 205. Metal sheet 200 defines a lengthwise direction L and a widthwise direction W. Additionally, metal sheet 200 has a first edge 201 and a second edge 202, each approximately perpendicular to lengthwise direction L.

In step 302, a plurality of grooves 274 are created in flat outer surface 204 of metal sheet 200. Grooves 274 run in lengthwise direction L of metal sheet 200 from first edge 201 to second edge 202 and are spaced apart in widthwise direction W. This may be accomplished e.g., by roll forming or stamp pressing grooves 274 into metal sheet 200. Roll forming is a process for shaping sheet metal, wherein the sheet metal is passed through a set of rolls mounted on one or more stands, each set of rolls performing bends in the sheet metal, incrementally if more than one sets of rolls are required. Stamp pressing, on the other hand, is a method for shaping a length of flat sheet metal wherein the sheet metal is placed between molding plates and then a large amount of pressure is applied to the molding plates to form the sheet metal into the desired shape.

With step 304, metal sheet 200 is rolled up in such a manner so as to form a cylindrically-shaped wall 276 of a tank 224 with grooves 274 on the outer surface of cylindrically-shaped wall 276. After metal sheet 200 is rolled up, grooves 274 may be aligned in such a way as to form continuous grooves around the exterior surface of the tank's cylindrically-shaped wall 276 as shown in step 306. This results in grooves 274 encircling tank 224 in a helical manner much like grooves 174 illustrated in FIG. 1. End portions 272 and 273 may also be added.

The present disclosure additionally provides a second method for making a tank with grooves. An exemplary aspect of this method generally includes providing a tank having a cylindrically-shaped wall, connected between a pair of end portions. The tank defining an axial and a radial direction and an exterior surface. The tank may be a steel tank. The method additionally includes creating or machining a plurality of grooves in the exterior surface of the tank, spaced apart in the axial direction. As above, this may be accomplished in a number of ways e.g., roll forming the grooves in the exterior surface of the tank's cylindrically-shaped wall. In one exemplary aspect of the above method, the grooves may be machined in such a way so as to form grooves that wrap around the exterior surface of the tank in a helical manner.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A water heater, comprising: a tank for holding water, said tank comprising a cylindrically-shaped wall connected between a pair of end portions, said tank defining axial, circumferential, and radial directions, the cylindrically-shaped wall having an exterior surface defining a plurality of circumferentially-extending grooves spaced-apart along the axial direction; and a refrigerant-based heating system configured for heating water in said tank, said heating system comprising a heat exchanger that includes a plurality of coils for the flow of heated refrigerant, the coils extend around said tank and are positioned within the plurality of grooves defined by the exterior surface of the cylindrically-shaped wall.
 2. A water heater as in claim 1, further comprising a thermal paste that affixes the coils to the grooves and enhances heat transfer.
 3. A water heater as in claim 1, wherein the coils are affixed to the grooves by welding the coils to said tank.
 4. A water heater as in claim 1, wherein the coils extend around said tank in a helical manner.
 5. A water heater as in claim 1, wherein said refrigerant based heating system is mounted to one of the pair of end portions of said tank.
 6. A water heater as in claim 1, wherein the grooves have a depth along the radial direction that is less than the diameter of the coils, so that the coils extend above the external surface of said tank.
 7. A water heater as in claim 1, wherein the grooves have a width along the axial direction approximately equal to the diameter of the coils.
 8. A water heater as in claim 1, wherein the coils are comprised of a metal.
 9. A water heater as in claim 1, wherein the coils are comprised of copper.
 10. A water heater as in claim 1, wherein said tank is comprised of a metal.
 11. A water heater as in claim 1, further comprising an outer jacket that surrounds the cylindrically-shaped wall of said tank and defines an annular space between the exterior surface of the cylindrically-shaped wall and said outer jacket.
 12. A water heater as in claim 11, further comprising insulation positioned in the annular space.
 13. A water heater as in claim 12, wherein the insulation comprises a foamed-in insulation.
 14. A water heater as in claim 1, a plurality of heat transfer features projecting along the radial direction from an interior surface of said tank, said heat transfer features extending longitudinally along the axial direction of the tank and providing additional surface area for heat transfer with water contained in said tank.
 15. A method for making a tank with grooves, comprising: providing a metal sheet having a desired thickness, the metal sheet having a flat outer surface, the metal sheet defining lengthwise and widthwise directions, and the metal sheet beginning with a first edge and ending with a second edge, each approximately perpendicular to the lengthwise direction; creating a plurality of grooves in the flat outer surface of the metal sheet, the grooves running in the lengthwise direction of the metal sheet, the grooves spaced apart in the widthwise direction, and the grooves beginning at the first edge of the metal sheet and ending at the second edge of the metal sheet; rolling up the metal sheet in such a manner so as to form a cylindrically-shaped wall of a tank, wherein the grooves are on the outer surface of the cylindrically-shaped wall; joining together said metal sheet in the form of the cylindrically-shaped wall of the tank; and adding a pair of end portions to complete the formation of the tank.
 16. A method for making a tank with grooves as in claim 15, further comprising the step of aligning the grooves of the first edge of the metal sheet with the grooves of the second edge of the metal sheet so as to form continuous grooves that extend along the outside of the cylindrical wall in a helical manner.
 17. A method for making a tank with grooves, comprising: providing a tank having a cylindrically-shaped wall connected between a pair of end portions, the tank defining axial and radial directions, the cylindrically-shaped wall having an exterior surface and an interior surface; and creating a plurality of grooves along the cylindrically-shaped wall of the tank, spaced apart along the axial direction, and providing grooves along the interior surface and exterior surface of the tank.
 18. A method for making a tank with grooves as in claim 17, wherein the grooves wrap around the cylindrically-shaped wall of the tank in a helical manner and have a rounded or semi-circular shape.
 19. A method for making a tank with grooves as in claim 17, wherein the metal sheet is comprised of steel.
 20. A water heater, comprising: a tank for holding water, said tank comprising a cylindrically-shaped wall connected between a pair of end portions, said tank defining axial, circumferential, and radial directions; a plurality of heat transfer features projecting along the radial direction from an interior surface of said tank, said heat transfer features extending longitudinally along the axial direction of the tank and spaced apart about the circumferential direction; said heat transfer features providing additional surface area for heat transfer with water contained in said tank; and a refrigerant-based heating system configured for heating water in said tank, said heating system comprising a heat exchanger that includes a plurality of coils for the flow of heated refrigerant, the coils extend around said tank on the cylindrically-shaped wall. 